example 2.6 pile in sand - eurocode 7 2/lecture 8 - exampl… · data for pile design 2nd...

PLEvaluation of Eurocode 7

PLEvaluation of Eurocode 7Example 2.6 PILE IN SANDETC 10

Bolesaw Kosiski

ETC 10Bolesaw Kosiski

Road & Bridge Research InstituteWarsaw, Poland

2nd International Workshop on Evaluation of Eurocode 7, Pavia, Italy, April 2010

GeneralGeneral


General

Designing in four steps:g g p1. Assessing of ground conditions, bearing layer,

minimal embedment of a pile.2. Choice of pile type, pile loadings, characteristic and

design parameters of ground layers, etc.3. Calculations a subject of this paper: ULS and SLS

of a pile, determining of pile length for given loadsor a number of piles neededor a number of piles needed.

4. Confirmation: experience, pile test loadings,monitoring of a pile construction and of a structure monitoring of a pile construction and of a structurethe only reliable verification of a design.


General: Eurocode 7 requirements

Limit states of a pile in compresionUltimate limit states (ULS)Ultimate limit states (ULS)- bearing resistance failure,

structural failure of the pile- structural failure of the pile- excessive settlement

Serviceability limit states (SLS)- excessive settlementexcessive settlement- vibrations


General: Eurocode 7 requirements

ULS compressive resistance from ground test resultsFc;d Rc;d

Model pile method(7.8)

The values of the correlation factors 3 and 4 depend on thenumber of profiles of tests, n.They may be set by the National annex the recommended valuesThey may be set by the National annex, the recommended valuesare given in Table A.10 of EC 7-1.


General: Eurocode 7 requirementsULS compressive resistance from ground test results

Alternative methodRb;k = Ab qb;k and Rs;k = As;i qs;i;k (7.9)Rb;k Ab qb;k and Rs;k As;i qs;i;k (7.9)

qb;k and qs;i;k are characteristic values of base and shaft resistance

Popular in several countriesmay need to be corrected by a model factor larger than 1,0g


General: Eurocode 7 proposals

Example models in EN 1997-2 in informative Annex Dl b fD.6: Correlation between compressive resistance of a

single pile and cone penetration resistance qcEmpirical data on q and q versus q resistance for pilesEmpirical data on qb and qs versus qc resistance for pilesin coarse-grained soils (from German Standard and EAPfhle - 2007)Pfhle 2007)

D.7: Method to determine the compressive resistance of aD.7: Method to determine the compressive resistance of asingle pile from cone penetration resistance qcFormulae and tables of empirical data on qb and qsb sversus qc resistance for piles in sands and gravely sandsand for clay, silt and peat (Dutch or Belgian method?)


Description of the Example 2 6Description of the Example 2.6


Fig. 2. Boring log and CPT resistance profile

Fig. 1. Data for pile design


Description of the Example 2.6 450 mm diameter piles bored with

p p 6

temporary casing founded in a medium dense to dense sand characteristic vertical loads: permanent of

300 kN and variable of 150 kN. small project - will be no load testing settlement will not govern the designsettlement will not govern the design

Using Eurocode 7 determine the designUsing Eurocode 7, determine the design length of the pile


Results of QuestionnaireResults of Questionnaire

E l 2 6Example 2.6


Results of Questionnaire Example 2.6 1st Phase: 12 solutions from five European countries (Germany 3, Italy 4, Poland 3, Portugal 1 and UK 1);one from Japan

2nd Phase (with the unified benchmark qc profile): 6 solutions (Germany 2, Italy 2, Poland 1, Portugal 1),

onl t o changed the res ltsonly two changed the results

Number of answers less than expected by the ETC 10Number of answers less than expected by the ETC 10.


Results of Questionnaire Example 2.6Main question was the pile length. It depends on:

- ground properties, pile shaft and base resistances- safety factors (partial, correlation and model)- calculation model - choice of characteristic values of geotechnical

parameters

Pile length:average 18 7maverage 18.7m

range 4.0m: min 17.0m (-9%), max 21.0m (+12%)


Results of Questionnaire Example 2.6Characteristic resistances: CPT qc, shaft qs and base qb; pile lengths

Pile length DsgnForceCPT qc resistance at depth Unit shaft resistance qs at depth Unit base resist. qbID g2.5 m 7.5 m 12.5 m 17.5 m 22.5 m 2.5 m 7.5 m 12.5 m 17.5 m 22.5 m 17.5 m 22.5 m m Fcd kN

1/72 6,00 2,80 2,20 16,00 14,50 30,0 17,5 0,0 60,0 72,5 5177 7488 19,5 6152/41 0,00 3,35 3,35 3.35 11,89 0,0 11,18 11,18 11,18 18,29 n/a 1189 20,0 6303/69 8,00 4,00 3,00 12,00 13,00 4,5 14,5 31,3 70,0 111,1 460 590 20,54/45 4 00 3 90 2 70 14 80 14 00 0 0 35 0 35 0 120 0 120 0 1800 1800 19 0 495

ID

4/45 4,00 3,90 2,70 14,80 14,00 0,0 35,0 35,0 120,0 120,0 1800 1800 19,0 4955/25 0,00 0,00 5,00 15,00 14,00 0,0 0,0 0,0 75,0 70,0 6580 7770 18,0 6306/83 7,40 3,60 2,50 13,50 13,50 74,0 51,7 111,0 125,0 125,0 2490 2490 17,0 n/a

StdDev 2,30 1,10 0,30 1,90 1,90 11,5 16,1 15,1 32,6 32,6 651 651 - -7/20 0,00 0,00 0,00 14,00 13,00 0,0 0,0 0,0 132,0 132,0 3773 3773 18,0 6308/51 5,00 4,00 2,50 13,00 13,00 12,0 22,0 0,0 75,0 75,0 3125 3125 21,0 6309/116 6,85 3,90 2,50 13,30 13,30 0,0 0,0 0,0 95,0 95,0 2720 2720 20,0 630/675

Benchmark qc values 98,0 98,0 2810 2810 19.5 67510/33 - 3,50 2,10 15,00 16,50 32,0 28,0 24,0 56,0 105,0 3100 - 17,5 63011/109 2 20 2 90 2 40 14 00 14 00 13 7 41 0 27 6 142 0 191 3 1622 2280 18 0 49511/109 2,20 2,90 2,40 14,00 14,00 13,7 41,0 27,6 142,0 191,3 1622 2280 18,0 495

Benchmark qc values - - 17.5 49512/91 5,00 3,50 2,20 16,00 14,50 12,2 26,7 53,5 75,4 96,4 3920 4936 18,0 61513/54 6,00 3,50 2,20 16,00 14,50 30,0 17,5 0,0 60,0 60,0 6600 8000 16,5 630

Total = 174,5 181,6 Total = 243,0M 14 4 13 9 M 18 69Mean = 14,54 13,97 Mean = 18,69


Results of Questionnaire Example 2.6 CPT qc resistance: - in upper layers large scatter, in many cases = 0;uppe aye s a ge scatte , a y cases 0;max values: 8MPa for 2.5m, 4 for 7.5m, 5 for 12.5m

- for 17.5m qc = 12 to 16; mean = 14.5MPaqc ;- for 22.5m qc = 11.9 to 16.5; mean = 14.0MPa

How did assessed these values? By eye - 8 cases 61.5% by statisical analysis - 3 cases 23% from a previous design - 1 case 8% other (average, Excell calc.) - 4 cases 31%


Results of Questionnaire Example 2.6What correlations did you used for soil parameters?

- unit weights of soils, relative density ID, relation qc to NSPT qc to friction angle, qc to su,qc SPT, qc g , qc u,

- selected sources: Standards BS, DIN, PN; German EA Pfhle; Manual (Kulhawy & Mayne); Robertson & Campanella 1983; Lunne, Robertson & Powell; Japan S f Hi h B id d P bli W k R hSpecs for Highway Bridges and Public Works Research Institute; Viggiani


Results of Questionnaire Example 2.6

Unit shaft resistance qs: in upper layers large scatter in many cases 0;- in upper layers large scatter, in many cases = 0;

max values: 74kPa for 2.5m, 52 for 7.5m, 111 for 12 5m111 for 12.5m

- for 17.5m qs = 60 to 142kPafor 22 5m q = 60 to 191kPa- for 22.5m qs = 60 to 191kPa

Unit base resistance qb: Unit base resistance qb: - for 17.5m qb = 1622 to 6600kPa- for 22 5m qb = 1189 to 8000kPafor 22.5m qb = 1189 to 8000kPa



Calculation model for shaft and base resistanceAnnex D 6 from EN 1997 2 2 cases 15%- Annex D.6 from EN 1997-2 2 cases 15%

- Annex D.7 from EN 1997-2 3 cases 23% Alternative in national annex/stand 3 cases 23%- Alternative in national annex/stand. 3 cases 23%

- Other (CPT, Bustamante-Gianeselli, static formula, Japan Highway Specs) 5 cases 38%Japan Highway Specs) 5 cases 38%



Which countrys National Annex was used?GB German Italian Polish PortugalGB, German, Italian, Polish, Portugal

Which Design Approach was used? Which Design Approach was used?DA1 Comb 1&2 5 cases 38%DA1 Comb 2 only 1 case 8%DA1 Comb 2 only 1 case 8%DA2 3 cases 23%DA2* (for piles = DA2) 2 cases 15% total 38%DA2 (for piles = DA2) 2 cases 15% total 38%DA3 1 case 8%Reliability Based Design RDB 1 case 8%Reliability Based Design RDB 1 case 8%


Results of Questionnaire Example 2 6Results of Questionnaire Example 2.6Partial safety factors, correlation and model factors

G Q f c cu s b t 3 41/72 1 Comb. 1 1,3 1,5 - - - 1 1,25 - 1,7 1,7 11/72 1 Comb. 2 1 1,3 - - - 1,45 1,7 1,6

Model factorCorrelation factors

ID DesignApproachPartial safety factors for ULS

2/41 1 Comb. 1 1,35 1,5 - - - 1 1,25 - - - 1,52/41 1 Comb. 2 1 1,3 - - - 1,3 1,6 -3/69 1 Comb. 1 1,35 1,5 1 1 - - - - 1,6 2 1,43/69 1 Comb. 2 1 1,3 1,25 1,25 - - - -4/95 1 Comb 1 1 3 1 5 1 1 1 1 1 1 7 1 74/95 1 Comb. 1 1,3 1,5 1 1 1 1 1 - 1,7 1,7 -4/95 1 Comb. 2 1 1,3 1 1 1 1,45 1,7 - 1,7 1,7 -5/25 2 1,35 1,5 - - - - 1,1 1,1 1,4 1,4 16/83 RBD - - - - - - - - - - -7/20 2 1,35 1,5 - - - - - 1,4 - - -8/51 1 Comb. 1 1,35 1,5 - - - 1 1,25 - 1,4 - 18/51 1 Comb. 2 1 1,3 - - - 1,3 1,6 -

9/116 2 1,35 1,5 - 1,5 - 1,4 1,4 1,4 - - -10/33 3 Comb. 1 1,35 1,5 1,25 - - 1,3 1,6 - 1,27 1,27 R(b,s)10/33 +Comb 2 1 1 3 1 6 1 310/33 +Comb. 2 1 1,3 - - - 1,6 1,3 -11/109 1 Comb.2 1 1,3 1,25 - 1,4 1,7 1,6 - - -12/91 2 1,3 1,5 1 1 1 1,15 1,35 1,3 1,7 1,7 113/54 2 1,35 1,5 - - - 1,1 1,1 1,1 - - -


Some of values given were not used in calculations


Values of partial factorsActions Actions

most to EC7-1 Ann. A: G =1.35 Q =1.5 8 cases 62%Ground resistances 1 (5) or 1 25 (3) Ground resistances f = 1 (5) or 1.25 (3)

c = 1 (5), 1.25 (1), 1.5 (1) cu = 1 (4), 1.4 (1)Shaft resistance = 1 to 1 6 Shaft resistance s = 1 to 1.6

Base resistance b = 1 to 1.7 Total resistance = 1 to 1 6 Total resistance t = 1 to 1.6 Correl. Factors 3 = 1 to 1.7, 4 = 1 to 2 Model Factor (2 cases) Rd = 1 4 (1) 1 5 (1) Model Factor (2 cases) Rd = 1.4 (1), 1.5 (1)



Design compresive forces FcdF 630 kN (7 cases)Fcd = 630 kN (7 cases)

615 kN (2 cases)495 kN (2 cases)495 kN (2 cases)n.a. (2 cases)

In GermanyIn Germany Fcd = 675 kN for structural design (acc. to EC2)


Results of Questionnaire Example 2.6 How conservative is your previous national practice?

Conservative 8 cases 61.5% About right 1 case 8%Unconservative 1 case 8%Very unconservative 1 case 8%

H i i EC7 i h N i l A ? How conservative is EC7 with your National Annex?Conservative 6 cases 46% Ab t i ht 4 31%About right 4 case 31%Very unconservative 1 case 8%


Results of Questionnaire Example 2.6 How does your EC7 design compare with your previous national practice?

M i 2 15%More conservative 2 cases 15%About the same 6 cases 46%L ti 3 23%Less conservative 3 cases 23%

Ha ing completed o r design to EC7 ho confident Having completed your design to EC7, how confident are you that design is sound?

Unsure 4 cases 31%Unsure 4 cases 31%

Confident 7 cases 54%Confident 7 cases 54%Very confident 2 cases 15%

=69%


Discussion of Results ofDiscussion of Results of Example 2.6Example 2.6


Discussion of Results of the Example 2.6

Pile shape and length

p

Pile shape and length 450 mm diameter piles bored with casing are

rather not typical in many countries CFA piles orrather not typical, in many countries CFA piles or piles with larger diameter would be used

A pile should be embedded in a competent layer at least e.g. 2.5m (EA Pfhle) or 3.0m (PL Standard) Therefore a pile shorter than 18m (17.5m?) may be regarded as not safe.


Discussion of Results of the Example 2.6Pile length: average 18.7m

4 0 i 17 0 ( 9%) 21 0 ( 12%)

p

range 4.0m: min 17.0m (-9%), max 21.0m (+12%)The scatter is small, considering variety of assumptions Design Approaches calculationassumptions, Design Approaches, calculation methods, safety factors etc.

Probably most people would intuitively just by looking at the CPTProbably most people would intuitively just by looking at the CPT result say, that the piles should penetrate the stiffer layer after 16 m a couple of meters. So would the scatter be (much) higher, if the cpt profile would have been more constant?if the cpt profile would have been more constant?

But bearing in mind the results of the Workshop in Dublin (2005) range of pile length 62%, ( ) g p g ,the final result seems surprisingly better than one may expect


Discussion of Results of the Example 2.6

Unit shaft resistance qs in softer upper layersI l h h f i i lIn several answers the shaft resistance in upper layers was fully disregarded or reduced.An experienced designer would assume there q 0An experienced designer would assume there qs = 0.

Calculation model for shaft and base resistanceIn several solutions model pile methodIn some cases Alternative method - from EN 1997-2 Annex D.6 and D.7 - from national annex or standards

h h d b d h (Other methods based on the CPT (e.g. Bustamante-Gianeselli)

Reliability Based Design RBD to Japan Highway Specs282nd International Workshop on Evaluation of Eurocode 7, Pavia, Italy, April 2010

Reliability Based Design RBD to Japan Highway Specs

Discussion of Results of the Example 2.6Design ApproachesDA chosen according to National Annexes

Almost equal use of DA1 and DA2 DA3 only 1 case

Partial & Model FactorsPartial factors to EC7-1 Annex A or to National Annexes. In two cases low PFs compensated by Model Factor

( 1 5 d 1 4)(= 1.5 and 1.4)

J R li bilit B d D i t tJapan answer: Reliability Based Design not to Eurocode but results very similar


Discussion of Results of the Example 2.6Benchmark soil data Fixing the benchmark soil profile data did not g pchange much the results. In 2nd phase only in 2 (of 6) answers the pile length was changed by 0.5m.

S ttl t f th il i SLSSettlement of the pile in SLSOnly four answers: 6.4, 13.7, 20 and 20.5 mmO l h fi b bl h hOnly the first two are probable, others are rather overestimated.

s = 20 mm = ca 4 4% of pile diameters = 20 mm = ca. 4.4% of pile diameter seems not probable in SLS


ConclusionsConclusions

E l 2 6Example 2.6


Conclusions Eurocodes should unify structural designing in EU. Itis a long way to achieve this goal

f l d d d In fact pile designing to Eurocode does not exist.There is much freedom in use of rules of Eurocodes.The reasons of discrepancy of results are: different The reasons of discrepancy of results are: different

understanding of characteristic values, three Design Approaches, various design models, variousApproaches, various design models, various traditions and specific features resulting in National Annexes of particular countries, etc. It is a good task for European geotechnical community: if not reach unified all calculations, thent l t hi bl l l f f t ( dat least achieve a comparable level of safety (and

economy!) of designs.


Thank you for your attention!


example 2.6 pile in sand - eurocode 7 2/lecture 8 - exampl… · data for pile design 2nd...

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